1. Field of the Invention
The present invention relates to an image reading apparatus which reads image information of an original while changing relative positions of the original and a reading sensor.
2. Description of the Related Art
In general, an image reading apparatus of this type which illuminates an original by a light source and reads an original image by a line image sensor or the like. However, due to the presence of a unevenness in light quantity of the light source and a unevenness in sensitivity of the line image sensor, shading correction must be performed by reading a white color reference member.
In reading of an original, in order to detects a boundary between an original and a background, to detect skew feed of the original, and to reduce transparent seeing of an image on the rear side of the original, the color of a member facing the line image sensor must be made a color except for white (in general, black).
A conventional image reading apparatus will be described below with reference to FIG. 6. In the image reading apparatus in FIG. 6, image information of both sides of an original D by reading units 111 and 112 in which line image sensors have been built. Before the image reading apparatus reads the original D, rotating arms 131 and 132 to which color reference members 121 and 122 have been fixed are rotated, the color reference members 121 and 122 are protruded from frames 141 and 142 and inserted between the reading units 111, 112 and the frames 141, 142. Thereafter the reading units 111 and 112 read the front surfaces of the color reference members 121 and 122. In this manner, correction data to perform shading correction of an output from the line image sensor is stored for each pixel.
Thereafter, in the image reading apparatus, the rotating positions of the rotating arms 131 and 132 are returned to normal positions. And images of original D are read by the reading units 111 and 112. In this case, in reading of the original D, with reference to correction data stored in advance, shading correction of the output from the line image sensor is performed.
Some image reading apparatus performs shading correction by using a roller-shaped color reference member without using a rotating arm (for example, see Japanese Patent Application Laid-open No. 2003-23531). The image reading apparatus rotates a color reference member in a reading operation of the color reference member to moderate an influence to correction data by scratches and stains on the color reference member.
However, in an image reading apparatus shown in FIG. 6, spaces are required to rotate the rotating arms 131 and 132. Since the apparatus must assure the space, a product disadvantageously increases in size.
Parts related to the rotating arms 131 and 132 and the rotating mechanism for the rotating arms increase the number of parts. For this reason, a parts cost and an assembly cost disadvantageously increase to prevent the price from being lowered.
The color reference members 121 and 122 are inserted into or removed from an original conveyance path. For this reason, the color reference members 121 and 122 are gradually scratched or stained in inserting and removing processes. When the scratches and the stains are conspicuous, cleaning and replacing of the color reference members 121 and 122 must be performed. However, since the color reference members 121 and 122 are fixed to the rotating arms 131 and 132, respectively, the rotating arms must be swung once in replacement and protruded form a frame. For this reason, the replacement is poor in operability.
In the image reading apparatus disclosed in Japanese Patent Application Laid-open No. 2003-23531, shading is less influenced even though the color reference member is scratched or stained. However, since the color reference member is large in size, a reduction in size of the product is limited.